FIG. 4 illustrates a continuous feed print engine as shown in co-pending U.S. patent application Ser. No. 12/560,483, filed Sep. 16, 2009, the disclosure of which is incorporated herein by reference in its entirety. A continuous feed print engine prints respective pages on a single, continuous sheet of media feed through the print engine. For example, in FIG. 4, a roll of material on which images are to be printed, for example, a roll of paper, is placed in the supply device. The unwinder feeds the roll of paper in a continuous stream through the printer in process direction P. The printer prints pages on the sheet and individual pages are cut from the sheet by the cutter. Instructions and data regarding control of the unwinder and the printing process are provided by the computer. Some continuous feed print engines, such as the engine in FIG. 4, are configured to print images onto both sides of the media, also referred to as duplex printing.
In FIG. 4, a web supply and transport system is configured to supply a very long (i.e., substantially continuous) web W of media (paper, plastic, or other printable material) from an unwinder 10. The web W may be unwound as needed, and propelled by a variety of motors, not shown, along a web path. A set of rollers 12 controls the tension of the web as the web moves through the path.
The imaging device of FIG. 4 is a duplex printer meaning that it is capable of printing images onto both sides of the continuous web. In an example embodiment, to enable duplex printing, the web transport system (and printing system) is a dual width, or dual path, transport system that is configured to transport two lengths of the web along the web path simultaneously. In an example embodiment, the rollers that transport and guide the web along the web path are at least twice the width of the web to accommodate the two lengths of the web. A first side of the web transport system is configured to transport a portion of the web W with one of the surfaces of the web facing in a direction to be printed upon by the printheads of the print station, also referred to herein as the printing, or process, direction. The second side of the web transport system is configured to transport a portion of the web with the opposite surface, i.e., the duplex surface, of the web facing the printing direction. The first or simplex side and the second or duplex side of the web transport system may also be referred to as the first or simplex web path and the second or duplex web path, respectively. The dual web path of the web transport system includes entrance roller(s) and an exit roller(s) 28.
The web transport system is configured to transport the web along the simplex and duplex web paths simultaneously and maintain consistent lateral positioning of the webs at least in the print zone so that images formed on the web are accurately registered. Any suitable method of registering or positioning of the webs along the dual path web transport system may be utilized. For example, edge sensors, as are known in the art, may be used to detect the edges of the webs, and suitable mechanisms for correcting or compensating for deviations of the web positions from desired positions may be used to adjust the lateral positions of the web at one or more positions along the dual web paths to ensure consistent and accurate positioning and/or spacing of the webs at least in the print zone. Also shown are printheads 22, midheaters 30, “spreader” 40, and rolls 42 and 44, and station 48.
In general, ink jet printing machines or printers include at least one printhead that ejects drops or jets of colorant, such as liquid ink, onto a recording or image forming media. A printhead includes a plurality of ink ejectors through which colorant is ejected onto the sheet. The ejectors can become clogged or otherwise fail to eject sufficient colorant. In this case, the volume of colorant ejected from adjacent or downstream ejectors can be increased in an attempt to compensate for the defective ejectors. However, the quality of the image on the portion of the sheet associated with the defective ejectors is inferior to the quality that properly operating ejectors would produce.